LONDON — A British warship forced three Iranian boats to back off after they sought to block a British tanker from passing through the Strait of Hormuz, the Defense Ministry said Thursday, in the latest escalation of tensions between Tehran and the West.
“Contrary to international law, three Iranian vessels attempted to impede the passage of a commercial vessel, British Heritage, through the Strait of Hormuz,” the British government said. “We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region.”
Iran denied any attempt to stop the tanker, according to Iranian news agencies.
Last week, British forces seized an Iranian tanker off the coast of Gibraltar bound for Syria, on suspicion that it was violating European Union sanctions, which Iran called an act of piracy. Some Iranian officials spoke of retribution, and an officer in Iran’s elite Revolutionary Guard, Mohsen Rezaei, wrote on Twitter that if the tanker were not released, Iran “will be duty-bound to take reciprocal action and seize a British oil tanker.”
The dispute Thursday is the latest complication in a three-way drama involving Iran, the United States and Europe that has played out since last year, when President Donald Trump abandoned the 2015 nuclear deal with Iran and restored sanctions that had been suspended under the deal.
Iranian President Hassan Rouhani had derided Britain as recently as Wednesday for its decision to send its warships to escort commercial vessels through the Gulf. Calling Britain “scared” and “hopeless,” Rouhani had warned that, “You, Britain, are the initiator of insecurity and you will realize the consequences later.”
Britain and other Europeans powers have sought to tamp down rising tensions between the United States and Iran, and salvage the nuclear pact. But Britain’s clashes with Iran could increase its own willingness to join the Trump administration in confronting Tehran, adding momentum to the conflict.
The most recent escalation began in May, after the Trump administration implemented comprehensive new sanctions intended to cut off all Iranian oil exports as part of an effort to pressure Tehran into accepting sweeping new restrictions on its military activities and its nuclear program.
In May and June, six tankers were attacked near the Strait of Hormuz, and Washington said Iranian forces planted naval mines to target some of the ships. The British government has said publicly Iran was “almost certainly” responsible for an attack last month on two tankers in the Gulf of Oman. Iran has denied responsibility.
The United States was on the verge of launching a missile strike against Iran in June in retaliation for the shooting down of a U.S. surveillance drone, but Trump said he called off the military action at the last minute.
In the tanker seizure near Gibraltar, Britain has said the ship was stopped because of EU sanctions against Syria, not because of U.S. sanctions against Iran. But Spanish and Iranian officials have said the British acted at Washington’s request.
In its statement Thursday, the British government said three Iranian boats had attempted to stop the British Heritage in the early morning as it headed toward the Strait of Hormuz, a narrow passage out of the Persian Gulf that is a vital channel for international oil supplies.
A British warship, the Montrose, had been escorting the tanker to guard against Iranian interference. After a short standoff, the British warned the three Iranian boats to back away and they did, the British government said in its statement.
“H.M.S. Montrose was forced to position herself between the Iranian vessels and British Heritage and issue verbal warnings to the Iranian vessels, which then turned away,” the Defense Ministry said in a statement.
Although Iran has long maintained that it does not seek a nuclear weapon, the United States and its Western allies have cited evidence that Tehran hid secret nuclear research moving in that direction. Before the 2015 nuclear deal, the international powers had imposed economic sanctions intended to pressure Iran to accept restrictions on its nuclear program. Those sanctions were lifted when Iran agreed to dismantle much of its nuclear program under the deal.
The Trump administration later declared those restrictions inadequate and vowed to force Iran to submit to more severe limits on a much broader range of activities, including its support for allied militias around the region.
Britain and the European Union, which also signed the 2015 accord, still support the agreement and have urged Iran to comply with it, while pleading with the Trump administration to return to it. The European governments have also sought to set up an alternative trading system that would allow Iran to sidestep the latest U.S. sanctions.
But the Trump administration has embarked on a campaign of “maximum pressure” that culminated in May with new sanctions seeking to cut off Iranian oil sales anywhere in the world, devastating the Iranian economy. Iranian officials called the penalties “economic warfare.”
After adhering to its obligations under the 2015 deal for more than a year after the United States withdrew, Tehran responded to the U.S. actions with carefully calibrated steps to revive its nuclear program beyond the limits imposed by the accord.
Over the last two weeks, Iran has exceeded the cap on its stockpile of low-enriched uranium and also begun enriching uranium to slightly higher levels than had been allowed under the deal. Both moves could be easily reversed if Iran decides to return to full compliance with the agreement, but could be small steps toward building a nuclear weapon.
Iran argues that its steps are authorized under the agreement because European governments have failed to deliver the promised sanctions relief. It says it will take additional steps in 60-day intervals unless the Western governments provide economic relief.
Under the terms of the accord, Britain or the other European nations could seek to trigger “snapback sanctions,” restoring the former economic penalties against Iran to punish it for exceeding the limits of the agreement. That would effectively extinguish hopes of reviving the deal.
The United States and some of its allies have also accused Iran of retaliating against the sanctions by threatening the flow of oil through the vital Persian Gulf shipping lanes — a vulnerable passage with Iran on one side and its U.S.-backed Arab rivals on the other.
The episode Thursday will increase alarms in the West that Iran might seek to cut off the flow of oil through the Gulf.
The U.S. military has said it will begin working with partners to escort more tankers through the Gulf.